Bill Schwab wrote:
In such a situation, how close to the edge of an Al part would you
consider it "safe" to tap for 4-40 and 8-32, respectively? Again, the
concern is not so much ultimate strength as robustness and common sense.
Ordinarily, I try never to get closer than 0.1" from the OD of the
hole to the edge, and usually think more about staying clear of
parallels, so this is new to me.

Thanks,

Bill

I've tapped a pair of 8/32 holes in the end of a 1/2" dia rod
so close to the edges that the thread telegraphed to the
surface and they held just great.
I didn't want the part being atached on the end to be able
to rotate. That is the reason for the thing. I had to turn
down the diameter of the heads to put the two screws in. :-)
...lew...